This work focuses on steroid receptors, including the androgen receptor (AR), the estrogen receptors (ERs) ERα and ERβ, known as the classical ERs, and GPR30, a recently described G protein-coupled estrogen receptor. Each of these receptors plays a role in many normal tissues and disease pathologies and signaling through steroid receptors is required for growth of many cancers. Additionally, many tissues express more than one estrogen receptor, making delineation of the functions of individual receptors difficult.
We have previously identified a GPR30-selective agonist, G-1, and this small molecule has been shown to mediate GPR30 function in a range of in vitro and in vivo systems. Thus, selective mediators of steroid receptor function do exist and will be useful in characterizing receptor function and in investigating therapeutic potential of each receptor individually. We hypothesize that the identification of novel estrogen and androgen receptor ligands will result in further elucidation of steroid receptor function in complex systems.
To address the possibility that additional selective ligands for steroid receptors exist, we first optimized a series of AR assays for investigation of a library of small molecules to search for novel AR-mediating functions. Subsequently, high-throughput screening was used to search for selective estrogen receptor ligands and this search identified a small molecule antagonist of GPR30, G15. Follow-up characterization of G15 as well as synthetic chemistry based on the structural similarities resulted in a second-generation GPR30 antagonist, G36, which has increased specificity for GPR30 versus ERα/ERβ. These compounds were used to probe the function of GPR30 in glioma and we find that GPR30 is the functionally important estrogen receptor in this system, regulating the response of glioma cells to both estrogen and tamoxifen. Finally, two series of GPR30-targeted in vivo imaging agents were generated and characterized for biological activity prior to small animal imaging.
This work demonstrates the necessary processes involved for small molecule discovery and characterization, as well as several applications for receptor-specific small molecules beyond their initial identification.